This invention relates to tubular film for encasing food products such as sausage and cheese. The invention more particularly relates to such casing material made from regenerated cellulose.
Food casings made from regenerated cellulose from xanthate viscose have been known for an extended period of time and can be made using methods well known to those skilled in the art. In particular, xanthate viscose is made by treating cellulose from cotton, wood, or other plant fiber with alkali followed by dissolving in carbon disulfide. The resulting viscose is then extruded through a die to form a tube. The resulting tube is then regenerated, usually by passing it through a coagulating bath containing coagulating materials such as sodium sulfate, and sulfuric acid. The casing is then dried.
U.S. Pat. Nos. 2,999,756 and 3,835,113 describe such processes in detail.
It is also known that cellulose containing casings can be made by extruding viscose onto a cellulose fiber web, usually a non-woven paper, shaped in the form of a tube, followed by regeneration. Such casings are known as "fibrous" casings.
It has been recently discovered that cellulose casings can also be made by precipitation (regeneration) from solutions of cellulose in a mixture of amine oxide and water. N-methyl morpholine amine oxide (NMMO) being a preferred amine oxide for this purpose.
The term "regenerated cellulose food casings" as used herein is intended to include both of the xanthate viscose and amine oxide types of casings.
Regenerated cellulose food casings have been successful for a number of reasons including relatively low cost, permeability to smoke, strength and dimensional stability.
Despite the advantages of regenerated cellulose food casings, there are a number of areas where properties could be improved. In particular, longitudinal dimensional stability is not as good as desired, especially when the casing is wet, i.e. a stuffed food casing will have unacceptable longitudinal stretch when hung vertically, e.g. in a smoke house or for purposes of curing. Such stretch can be as much as ten percent or more.
While regenerated cellulose food casings have fair permeability, it is still not as good as desired. And in order to obtain sufficient strength, the wall of the casing has been thicker than desired. Thicker walls use more viscose material than desired, decrease permeability, and reduce the quantity (unshirred length) of casing that can be shirred (longitudinally folded and compressed) into a standard unit of shirred length.
Attempts have been made to make such casings with thinner walls by variation of processing conditions, e.g. chemical changes in the regenerating bath as described in U.S. Pat. No. 4,590,107. Unfortunately, such thin wall casings have had insufficient burst strength and tensile strength for commercial application.